Highly active, "clean" and stable PdCo nanodots anchored on graphene is successfully synthesized using an in-situ adsorption-reduction method, exhibiting the highest peak current density (up to 1362.1 mA mg(-1)) toward formic acid oxidation over previously published PdCo based alloy catalysts under the same characterization conditions. The nanodots could keep their original size and dispersity even after 200 cycles electrochemical test. This work not only demonstrates a universal in-situ adsorption-reduction route to preparing an active electrocatalyst toward formic acid oxidation for direct formic acid fuel cells but also offers new opportunities to design and synthesis of noble metal alloy based nanodots with improved electrocatalytic performance for energy conversion/storage and sensor systems.